21st March 2017, Paris
During JEC World 2017 in Paris, Inside Composites talked to Frank Kerstan, Global Programme Manager for Automotive Composites at Henkel.
Inside Composites: In what ways is Henkel – as a resins and adhesives specialist – helping car manufacturers to find new ways to reduce weight and gain fuel efficiency?
Frank Kerstan: As vehicle manufacturers worldwide look to reduce weight from their cars and trucks to help boost fuel economy and reduce emissions, they find themselves challenged to set aside the mind-set that has dictated traditional material and process choices and look openly at new and emerging technologies. This includes such seemingly mundane topics as adhesives and other joining options. Each car today contains, on average, 15 kg of adhesives – and the prospects are excellent for their increased penetration into the vehicles of tomorrow. Components such as instrument panels, bumpers, windscreen wipers, gears and the cross members on frames are all secured in place by various types of adhesives.
So adhesives technology is becoming more of a consideration in the equation?
FK: Yes, because automakers are increasingly turning to polymer-based composites to replace steel and aluminium and this creates a growing need to find effective ways to bond these types of mixed materials to one another. In some applications, adhesives need to provide structure and rigidity, and in others they need to be flexible and pliable – all while providing a nearly unbreakable bond.
Isn’t welding preferable?
FK: It might seem counter-intuitive, but testing has shown that adhesive bonds are more stable than welded joints. This makes them viable options in such demanding uses as on frame cross members. As a result, more vehicle makers are turning to adhesive bonding instead of the more traditional joining methods of welding and riveting. Adhesives also can help to seal scratches and joints, while also reducing noise.
What are the challenges facing designers of hybrid multi-substrate systems in modern, lightweight automobile bodies?
FK: Well, a major one is how to overcome the different coefficients of thermal expansion (CTE) when creating bonds that must last for many years between these very different materials. The market needs an adhesive that offers both high strength and high elasticity at the same time. In answer to this need, Henkel developed the new adhesive Loctite UK 2015, which is based on two-component polyurethane technology. This adhesive is ideally suited for use on structural body parts, regardless of whether they are made of fibre-reinforced plastics, e-coated steel or e-coated aluminium.
Can you give us an example of composites making gains over steel?
FK: One is that recently implemented by Volvo for use in its new top-line, crossover SUV model, the XC90, as well as in its premium V90 estate and S90 models. Henkel partnered with Austrian automotive composites specialist Benteler-SGL to redesign the vehicles’ rear suspensions.
What was the aim?
FK: It was to replace the usual helical springs mounted on the rear axle and the team involved did this by using high-pressure resin transfer moulding, or HP-RTM, to produce lightweight leaf springs made from an advanced, glass-fibre-reinforced polymer composite material.
The transverse leaf spring enables a more compact axle design than with the bulky helical steel springs it is replacing. The transverse leaf spring allows the elimination of the coil springs, which means the axle protrudes less into the trunk area, leaving more loading space. In addition, the new design provides a smoother ride and improved NVH (noise, vibration, harshness) behaviour.
Even more important is that the composite leaf spring offers significant weight savings compared with their metallic counterparts. The new axle system weighs 4.5 kg less than the conventional helical spring construction.
Henkel’s flagship product, the Loctite Max 2 two-component polyurethane composite matrix resin system, is what enabled Benteler-SGL to develop these innovative leaf springs. Loctite Max 2 has very low initial viscosity, which enables fast injection of the resin into the mould and excellent penetration between the tightly-packed reinforcing glass fibres.
How does this compare to standard epoxy resins?
FK: Once injected into the mould, the matrix resin cures very quickly – much faster than standard epoxy resins – and for demould times, as low as one minute per part. The production system installed at Benteler-SGL, which uses a multi-cavity tool, is designed for a production output of more than 100,000 pieces per year. Last year, Benteler-SGL produced close to 100,000 composite leaf springs, and is projecting a figure of around 200,000 for 2017.
That’s very impressive. What other applications in automotive and beyond are you now targeting with these composites matrix resins and adhesives?
FK: Structural parts such as body components, for example, exterior paintable parts such as a roof, and chassis and powertrain components, including carbon fibre reinforced wheels, and drive shafts. Across numerous industries, the ability to leverage process know-how while also integrating and matching products within an overall package is essential for successfully applying this type of lightweight technology.
An openness to exploring non-traditional processes, materials and system design is already paying dividends for Volvo, and other vehicle makers have indicated their intention to adopt the same axle technology.
Henkel has also introduced a new binder technology, Loctite FRP 2000. What are its chief benefits?
FK: It has excellent compatibility with polyurethane and epoxy matrix resins and in the preforming process only small amounts of the binder are needed, thanks to its high mechanical strength. It is also well suited for complex-shaped parts. We also offer various auxiliary products in our Loctite Frekote mould range, including mould cleaners and release agents. All are highly suited for use with Loctite Max resins in closed-mould processes such as resin transfer moulding (RTM).
So what’s next for the company, in terms of development activity for the automotive industry?
FK: We continue to work hard to further develop resins, binders and multi-substrate adhesives that can be incorporated within new composite concepts and contribute to optimising the production process.
Last year we opened the Composite Lab, a state-of-the-art test facility, in Heidelberg, Germany. Here automotive customers can work with our experts to develop and test composite parts, and also optimise production process conditions. They can carry out trials on Henkel’s own HP-RTM equipment, which has resin injection units for polyurethanes and epoxies coupled to a 380-ton press. There’s much more to come from us for this sector.